I think for Start of reporting I change the field from text to calculation and add get(Currentdate). I think this is right.

But for End of reporting = two months before start of reporting how to I enter this. I thought of calculation as well and then the date option and enter in the date from today in two months, but then this doesn't seem like it will be dynamic, so I would need to change this date every day, as in two months todays date and that date would be the same.

You need to set up a script trigger. In layout mode, under Layouts, click on layout setup and you will see tab called "Script triggers". You need to write a script similar to :-

set variable $today= get(currentdate)

Set field start_of_reporting = $today

set field end of Reporting = $today - 60.

call it "Calculate dates" then (see screenshot) click the box "OnlayoutEnter" and specify your script. Note that start of reporting and end of reporting need to be dates NOT calculated fields if you do it this way. They also need to be Global.

Instead of global fields, you could use unstored calculation fields that use Get ( CurrentDate ):

cToday: Get ( CurrentDate )

cTwoMonths: Get ( CurrentDate ) + 60

This avoids the need for a script, but also locks you in to always using the same interval. If you use the scripted method, you have the option of also being able to specify different date intervals besides the 60 day interval.